The present invention relates to a method of manufacturing a product formed with a large number of parts, such as a magnetic storage device, a multi-chip module, liquid-crystal display device, printed circuit board, automobile, or electrical household appliance.
Manufacturing processes for a high-technology hardware product such as a magnetic storage device, multi-chip module, or liquid-crystal display device, generally consist of the parts-forming processes that require thin-flim forming, polishing, and other fine processing, and an assembly process for assembling completed parts. A magnetic storage device, for example, is manufactured by forming its major components, namely, a plurality of magnetic heads and disks in different parts-forming processes and then assembling each magnetic head and disk with a spindle motor, a frame, and other components in an assembly process to complete the device as a product. Also, a multi-chip module is manufactured by forming a plurality of chips on individual wafers in a parts-forming process and then extracting chips from different wafers, mounting the extracted chips mixedly on a wiring substrate or the like, connecting the wiring, and sealing all necessary sections with resin, ceramics, or the like, in an assembly process to complete the device as a product.
During the parts-forming processes and assembly process for manufacturing such a high-technology device, many characteristic values of its components are measured and managed using a technique referred to as SPC (Statistical Process Control). This technique is described in related literature such as “How to Create and Utilize Better Control Charts”, a book published by the Japanese Standards Association in 2001, “W. A. Levinson: Statistical Process Control in Microelectronics Manufacturing, Semiconductor International, November, pp. 95-102 (1994)”, and “L. S. Nelson: Interpreting Shewhart X-bar Control Charts, Journal of Quality Technology, Vol. 17, No. 2, pp. 114-116 (1985)”. SPC is used to analyze changes in chronologically arranged characteristic data and judge whether process abnormalities are occurring, and each characteristic value is independently managed during SPC.
However, it may be difficult to manage each characteristic value independently, and thus, alternative methods to SPC have been proposed. These alternative methods are intended to implement quality control that includes product defect detection, by converting each of process-by-process characteristic data measurements into Mahalanobis distance, a single evaluation measure, or into a statistical distance called Hotelling T2 or the like. The alternative methods are described in Japanese Patent Laid-Open Nos. 2000-114130, 2002-318617, Hei 11-339089, 2004-77188, and 2004-199501, and in related literature such as “Shoh-ichi Tejima and Masahiro Azemoto: Development of a Real-Time Monitoring and Diagnosing System Based on MT System Technology, 11th Quality Engineering Research Papers Presentation Convention, Quality Engineering Society of Japan, pp. 226-229 (2003)”, “Technological Development in MT Systems”, a book published by the Japanese Standards Association, “R. L. Mason: A Practical Approach for Interpreting Multivariate T2 Control Chart Signals, Journal of Quality Technology, Vol. 29, No. 4, pp. 396-406 (1997)”, and “Masashi Nakatsugawa, Masato Yamamoto, and Azuma Oh-uchi: The Mahalanobis Distance in MTS, Quality Engineering, Vol. 8, No. 5, pp. 19-26 (2000)”.
The present inventors considered it possible to realize the manufacture of a less expensive product with maintained high quality or high yield by applying any one of the above-mentioned statistical distances to production control. As far as the inventors were able to examine, Japanese Patent Laid-Open No. 2004-145390 was confirmed that describes an example of application of a statistical distance to production control. A method of controlling production by applying a statistical distance to the adjustment of manufacturing process parameters is described in Japanese Patent Laid-Open No. 2004-145390.
In recent years, magnetic storage devices, multi-chip modules, liquid-crystal display devices, printed circuit boards, and other high-technology devices have become more sophisticated in manufacturing process and are facing a situation under which, even if individual components satisfy predefined characteristic data, a completed product does not always become a nondefective product without fail.